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tabs(1)                                General Commands Manual                               tabs(1)



NAME
       tabs - set tabs on a terminal

SYNOPSIS
       tabs [options]] [tabstop-list]

DESCRIPTION
       The  tabs  program  clears  and  sets  tab-stops  on  the  terminal.   This uses the terminfo
       clear_all_tabs and set_tab capabilities.  If either is absent, tabs is  unable  to  clear/set
       tab-stops.  The terminal should be configured to use hard tabs, e.g.,

           stty tab0

       Like clear(1), tabs writes to the standard output.  You can redirect the standard output to a
       file (which prevents tabs from actually changing the tabstops), and later cat the file to the
       screen, setting tabstops at that point.

       These  are hardware tabs, which cannot be queried rapidly by applications running in the ter‐
       minal, if at all.  Curses and other full-screen applications may use hardware tabs  in  opti‐
       mizing their output to the terminal.  If the hardware tabstops differ from the information in
       the terminal database, the result is unpredictable.   Before  running  curses  programs,  you
       should either reset tab-stops to the standard interval

           tabs -8

       or  use  the reset program, since the normal initialization sequences do not ensure that tab-
       stops are reset.

OPTIONS
   General Options
       -Tname
            Tell tabs which terminal type to use.  If this option is not given, tabs  will  use  the
            $TERM environment variable.  If that is not set, it will use the ansi+tabs entry.

       -d   The  debugging  option  shows  a ruler line, followed by two data lines.  The first data
            line shows the expected tab-stops marked with asterisks.  The second data line shows the
            actual tab-stops, marked with asterisks.

       -n   This  option  tells  tabs  to check the options and run any debugging option, but not to
            modify the terminal settings.

       -V   reports the version of ncurses which was used in this program, and exits.

       The tabs program processes a single list of tab stops.  The last option to be processed which
       defines a list is the one that determines the list to be processed.

   Implicit Lists
       Use  a single number as an option, e.g., “-5” to set tabs at the given interval (in this case
       1, 6, 11, 16, 21, etc.).  Tabs are repeated up to the right margin of the screen.

       Use “-0” to clear all tabs.

       Use “-8” to set tabs to the standard interval.

   Explicit Lists
       An explicit list can be defined after the options (this does not use a “-”).  The  values  in
       the list must be in increasing numeric order, and greater than zero.  They are separated by a
       comma or a blank, for example,

           tabs 1,6,11,16,21
           tabs 1 6 11 16 21

       Use a “+” to treat a number as an increment relative to the previous value, e.g.,

           tabs 1,+5,+5,+5,+5

       which is equivalent to the 1,6,11,16,21 example.

   Predefined Tab-Stops
       POSIX defines several predefined lists of tab stops.

       -a   Assembler, IBM S/370, first format
            1,10,16,36,72

       -a2  Assembler, IBM S/370, second format
            1,10,16,40,72

       -c   COBOL, normal format
            1,8,12,16,20,55

       -c2  COBOL compact format
            1,6,10,14,49

       -c3  COBOL compact format extended
            1,6,10,14,18,22,26,30,34,38,42,46,50,54,58,62,67

       -f   FORTRAN
            1,7,11,15,19,23

       -p   PL/I
            1,5,9,13,17,21,25,29,33,37,41,45,49,53,57,61

       -s   SNOBOL
            1,10,55

       -u   UNIVAC 1100 Assembler
            1,12,20,44

   Margins
       A few terminals provide the capability for changing their left/right margins.  The tabs  pro‐
       gram has an option to use this feature:

       +m margin
            The effect depends on whether the terminal has the margin capabilities:

            •   If the terminal provides the capability for setting the left margin, tabs uses this,
                and adjusts the available width for tab-stops.

            •   If the terminal does not provide the margin capabilities, tabs imitates the  effect,
                putting  the  tab stops at the appropriate place on each line.  The terminal's left-
                margin is not modified.

            If the margin parameter is omitted, the default is 10.  Use +m0 to reset the  left  mar‐
            gin,  i.e.,  to  the left edge of the terminal's display.  Before setting a left-margin,
            tabs resets the margin to reduce problems which might arise on moving the cursor  before
            the current left-margin.

       When setting or resetting the left-margin, tabs may reset the right-margin.

PORTABILITY
       IEEE  Std  1003.1/The  Open Group Base Specifications Issue 7 (POSIX.1-2008) describes a tabs
       utility.  However

       •   This standard describes a +m option, to set a terminal's left-margin.  Very  few  of  the
           entries   in   the   terminal  database  provide  the  smgl  (set_left_margin)  or  smglp
           (set_left_margin_parm) capability needed to support the feature.

       •   There is no counterpart in X/Open Curses Issue 7 for this utility, unlike tput(1).

       The -d (debug) and -n (no-op) options are extensions not provided by other implementations.

       A tabs utility appeared in PWB/Unix 1.0 (1977).  There was a  reduced  version  of  the  tabs
       utility  in  Unix  7th edition and in 3BSD (1979).  The latter supported a single “-n” option
       (to cause the first tab stop to be set on the left margin).  That option is not documented by
       POSIX.

       The  PWB/Unix  tabs  utility,  which  was included in System III (1980), used built-in tables
       rather than the terminal database, to support a half-dozen hardcopy terminal (printer) types.
       It  also  had built-in logic to support the left-margin, as well as a feature for copying the
       tab settings from a file.

       Later versions of Unix, e.g., SVr4, added support for the terminal database, but kept the ta‐
       bles  to support the printers.  In an earlier development effort, the tab-stop initialization
       provided by tset (1982) and incorporated into tput uses the terminal database,

       The +m option was documented in the Base Specifications Issue 5 (Unix98, 1997),  and  omitted
       in  Issue  6 (Unix03, 2004) without documenting the rationale, though an introductory comment
       “and optionally adjusts the margin” remains, overlooked in the removal.  The documented  tabs
       utility  in  Issues  6 and later has no mechanism for setting margins.  The +m option in this
       implementation differs from the feature in SVr4 by using terminal  capabilities  rather  than
       built-in tables.

       POSIX  documents  no  limits on the number of tab stops.  Documentation for other implementa‐
       tions states that there is a limit on the number of tab stops (e.g., 20  in  PWB/Unix's  tabs
       utility).   While some terminals may not accept an arbitrary number of tab stops, this imple‐
       mentation will attempt to set tab stops up to the right margin of the screen,  if  the  given
       list happens to be that long.

       The  Rationale  section  of  the POSIX documentation goes into some detail about the ways the
       committee considered redesigning the tabs and tput utilities, without proposing  an  improved
       solution.  It comments that

            no  known  historical  version  of tabs supports the capability of setting arbitrary tab
            stops.

       However, the Explicit Lists described in this  manual  page  were  implemented  in  PWB/Unix.
       Those provide the capability of setting abitrary tab stops.

SEE ALSO
       infocmp(1), tset(1), ncurses(3NCURSES), terminfo(5).

       This describes ncurses version 6.3 (patch 20211021).



                                                                                             tabs(1)